JP3060245B2 - Endoscope illumination optical system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an illumination optical system for an endoscope.

[0002]

2. Description of the Related Art An illumination optical system of a general endoscope is provided with a negative lens having a concave surface on the light guide side in front of an exit end face of the light guide. It expands to illuminate the entire field of view of the observation optical system. The illumination optical system having such a configuration has a drawback that light refracted by the concave surface of the lens hits the side surface of the lens, emits light randomly, and disappears. .

In order to solve this disadvantage, Japanese Utility Model Application Laid-Open No.
The illumination optical system described in Japanese Patent No. 17071 discloses a concave lens of a negative lens, a central portion having a spherical shape and a conical surface outside the concave portion, and a refraction angle of a ray having a high ray height among rays emitted from a light guide. Is reduced to prevent light from hitting the side of the lens and disappearing. However, because of the limited shape of the combination of the spherical surface and the conical surface, the light distribution cannot be freely controlled, and some light sources to be combined have uneven illumination.

Further, as an illumination optical system for improving light distribution, an illumination optical system disclosed in JP-A-63-394415 and an illumination optical system disclosed in JP-A-64-3616 are disclosed. Optical systems are known.

[0005] These illumination optical systems are described in Japanese Utility Model Application Publication No.
Improving the light distribution of the entire field of view by appropriately setting the refraction angle according to the ray height of the light emitted from the light guide using an aspherical surface having a more complicated shape than the illumination optical system described in -17071 It was done.

The optical system disclosed in JP-A-64-3616 has the configuration shown in FIG. 16, and the light distribution is as shown in FIG. In this figure, the horizontal axis represents the light beam height of light emitted from the light guide in parallel to the optical axis, and the vertical axis represents the angle between the light beam refracted by the negative lens and the optical axis. Hereinafter, a diagram showing the relationship between the ray height h and the refraction angle A as in this diagram will be referred to as an hA characteristic diagram.

[0007] As can be seen from the above figure, in this conventional example, when the ray height is a predetermined value or more, the refraction angle is reduced with an increase in the ray height, and the degree of the decrease is appropriately determined. Light distribution is realized.

However, a sufficient light distribution can be obtained even by such a method up to an angle of view of about 120 °, and when the angle of view is very wide, the peripheral light quantity is not sufficient, and illumination unevenness tends to occur. Has disadvantages.

As a means for solving this drawback, it is conceivable to prevent light rays from being irregularly reflected on the side surface of the negative lens. FIG. 18 is a diagram showing a configuration for preventing the above-mentioned irregular reflection.

In the optical system shown in FIG. 18, since the negative lens placed in front of the light guide 1 is made of a single fiber 2, even if a ray having a high ray height is refracted by a concave surface and hits the side of the lens, The light is totally reflected at the boundary surface between the core 3 and the clad 4 of the single fiber 2 and travels toward the opposite side of the visual field. Therefore, the refraction angle can be increased with the height of the light beam, and the light can reach the periphery of the visual field.

FIG. 19 is an hA characteristic diagram of an illumination optical system using a single fiber as an illumination lens. Here, the horizontal axis is a value normalized by the maximum value hmax of the height of the light beam emitted from the light guide in order to set the maximum value to 1. The portions indicated by thick lines in the figure correspond to the portions which have been lost due to the irregular reflection.

As can be seen from FIG. 19, the refraction angle continues to increase as the ray height increases, so that the illumination light reaches a very wide range. The maximum value of the refraction angle is an angle determined by the numerical aperture of a single fiber. Here, the angle determined by the numerical aperture of a single fiber is the angle given by the following equation, where n0 and n1 are the refractive indices of the core and cladding of the single fiber, and n is the refractive index of the space from the single fiber to the object. A0. ^{[(N0) 2 - (n1} ) 2] 1/2 = nsin A0 above but allows a wide range illumination of the optical system, not sufficient with respect to the light distribution (light intensity distribution). FIG. 21 shows this state. For quantitative evaluation, an example using an illumination lens having the following data will be described. r = 1.272, n0 = 1.8, n1 = 1.
52, A0 = 74.6 ° hmax = 1.105 In the above data , r is the radius of curvature of the concave surface of the illumination lens, and n0 is
Refractive index of the core , n1 is the refractive index of the cladding, A0 is when the ray height is 1 (the ray height is normalized with the maximum value being 1)
Is the refraction angle. The exit surface of the illumination lens is a flat surface.

In the curves of FIG. 20, S1 is for the illumination lens of the above data .

Since the densities of the light rays included in the range of the light height Δh of the light emitted from the light guide can be considered to be the same at any ray height, if dh / dA is calculated, the light rays emitted in that direction can be almost determined. Strength. FIG. 21 illustrates this. In this figure, dh / dA is multiplied by cos ³ A in order to convert the light intensity as described above into a planar intensity, and this is normalized with the intensity at a refraction angle of 0 ° (axial intensity) as 1. The vertical axis indicates the calculated value, and the horizontal axis indicates the exit angle (refraction angle).

As shown by a curve b in this figure, the light intensity sharply decreases as the refraction angle A increases, and the periphery of the visual field becomes significantly darker than the center.

[0016]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an endoscope illumination optical system having good light distribution characteristics over a very wide viewing angle.

[0017]

The endoscope illumination optical system of the present invention has a basic configuration as shown in FIG.
An illumination lens is arranged on the object side of the light guide or the emission end of the light emitting element, and the illumination lens is made of a single fiber having at least one aspheric surface, and satisfies the following conditions. Within the range of 0 <h <1, (1) When d ² A / dh ² ≦ 0, A (h1) ≠ A (h2) (2) When d ² A / dh ² > 0 , A (h1) = A (h2) Here, h is a value obtained by normalizing the ray height of a ray emitted in parallel to the axis of the light guide with the maximum ray height, and h1 and h2 are different arbitrary values of h. (h1 ≠ h2) and A (h) are the refraction angles measured from the optical axis after passing through the single fiber lens when the ray parallel to the axis of the light guide has the ray height h.

FIG. 2 shows several patterns of the hA characteristic curve. Of the curves in this figure,
Curve a shows a curve in which the refraction angle increases linearly with the ray height, curve b shows a curve in which the refraction angle increases while decreasing the refraction angle in a portion where the ray height is large, and curve c shows a curve at a certain ray height. The curve d is similar to the curve c, and the tendency of the decrease is more remarkable, and the refraction angle becomes zero (parallel to the axis) at the maximum ray height. Each of the curves a to d is represented as follows. (Curve a) A = 70 ° h (Curve b) A = 70 ° sin (π / 2h) (Curve c) A = 70 ° sin (π / 1.25h) (Curve d) A = 70 ° sin (πh) FIG. 3 shows the light distribution intensity calculated based on FIG. 2 in the same manner as in FIG.

In the illumination system having characteristics such as curves c and d in FIG. 2, there is a portion where two ray heights correspond to one refraction angle A. This means that the light emitted from the two parts of the light guide illuminates the object at the same viewing angle. Therefore, the illumination light amount increases in the area where the light is irradiated twice, which may cause large uneven illumination.

For example, in the case of the characteristic having the curve c in FIG. 2, up to a refraction angle of 40 °, light with a small h, that is, light emitted from the center of the light guide, is irradiated.
In the above-mentioned region, the light is double-irradiated with the light emitted from the orbicular portion except the central portion of the light guide. For this reason, the illumination light amount sharply increases around 40 °, resulting in an intensity distribution having an intermediate peak such as 6 ′ shown by a curve c in FIG.

As described above, the curve c in the intensity distribution of FIG.
It is desirable to have a characteristic such as b and d that the strength gradually decreases.

In order to obtain a desired light distribution by making the refraction surface of the illumination lens aspherical, a curve d in FIG.
When the hA characteristic as described above is to be provided, the aspherical shape becomes a very complicated shape, and it is difficult to actually manufacture it. Therefore, in consideration of practicality, the intensity distribution as shown by the curves a and b in FIG. 3 can be realized by an aspheric surface whose curvature gradually decreases as the distance from the optical axis increases and has no inflection point in the middle. Therefore, the production of the aspherical surface is easy and practical.

Characteristics such as curves a, b, c and d are 0 <
Within the range of h <1, d ² A / dh ² ≦ 0 is satisfied.
The curves a and b further have the condition that they have no extreme value in the range of 0 <h <1.

The above condition is that any value of h different from h1,
When h2 (that is, h1 ≠ h2), it means that the relationship of A (h1) ≠ A (h2) is satisfied. Therefore, in order to have the characteristics shown by the curves a and b, The following condition should be satisfied. That is, 0 <Within h <1, the light distribution unevenness by satisfying the above conditions as in A (h1) ≠ A (h2 ) than when ^{d 2 A / dh 2 ≦ 0} , and h1 ≠ h2 It is possible to obtain a good illumination optical system without any problem.

Next, a description will be given of an illumination optical system of the type in which the refraction angle continues to increase (at least does not have a decreasing tendency) with an increase in the light beam height.

An illumination optical system of this type has an hA
If the characteristic curve has an inflection point on the way, it is difficult to form a locally bright portion, and it is difficult to cause uneven light distribution. Therefore, it is desirable to set such that the hA characteristic curve has an inflection point.

When setting is made so as to have an inflection point as described above, it is assumed that d ² A / dh ² > 0 is satisfied in a region excluding the inflection point. consider. When the above condition is satisfied, the angle of refraction increases as the ray height increases, and the density of illumination light around the field of view decreases. Therefore, simply expanding the light beam usually darkens the area around the field of view.

Therefore, in the above case, it is desirable to have the hA characteristic as shown in FIG. This characteristic curve is such a characteristic that the refraction angle increases again with an increase in the ray height. A typical configuration for realizing this characteristic is a lens having a stepped two spherical surface as shown in FIG.

In order to explain to some extent quantitatively, a lens having the following data is used as an example. R1 = 1.272, R2 = 0.855, h1 = 0.74
1, h2 = 1.105, n0 = 1.8, n1 = 1.52, A
0 = 74.6 ° where R1 is the radius of curvature of the sphere at the center of the refractive surface of the illumination lens, R2 is the radius of curvature of the sphere outside the center, h1 is the radius of the sphere at the center, and h2 is the outer sphere. Is the radius of the outer circumference. Also, n0, n1, and A0 are the refractive index of the core , the refractive index of the clad, and the refraction angle when the ray height is 1, respectively, as described above.

FIG. 6 shows the light distribution characteristics of an illumination optical system using this illumination lens, similarly to FIG. In this figure, S2 shows the light distribution characteristics on a spherical object at the center of the illumination lens, and S1 shows the intensity distribution on the spherical object at the periphery of the illumination lens.

As can be seen from this figure, although there is a slight bulge in the middle, the light distribution characteristic has a tendency to gradually decrease as the ray height increases as a whole, indicating that the uniformity of the light distribution is good. . This can be realized by supplementing the light amount around the visual field, which is insufficient with the curve S2 alone, with the curve S1.

That is, within the range of 0 <h <1, h-
When the A characteristic curve has an inflection point and satisfies d ² A / dh ² > 0, an illumination system with good light distribution characteristics can be obtained.

The fact that the hA characteristic curve has an inflection point means that A (h1) = A when any two values of h are h1, h2 (h1 ≠ h2).
(h2) Since the relationship is the same, the above condition is as follows.

Within the range of 0 <h <1, d ² A / dh ² >
In other words, when 0 and h1 ≠ h2, the relationship of A (h1) = A (h2) holds. In the end, the above is true for d ² A / dh ² > 0 and any different values of h, h1, h2 (h1 ≠ h2), within the range of 0 <h <1.
A condition for obtaining a favorable illumination system is to include a portion where the relationship of (h1) = A (h2) is satisfied, that is, to satisfy the above condition (2).

Although the illumination optical system of the present invention has been described relatively qualitatively, in order to obtain the above light distribution characteristics,
This can be realized by using an aspherical surface as the refraction surface of the illumination lens.

As is apparent from the above description, the feature of the present invention is that an illumination lens has a single fiber, one surface of which is an aspheric surface, and the conditions (1) and (2) are obtained by using this aspheric surface. ) Has a light distribution characteristic including a portion satisfying (3).

The above description has been given of an illumination optical system which can provide a great effect by using an illumination lens in which an aspheric surface is formed on a single fiber in combination with an observation system having a field angle of 120 ° to 150 °. However, an observation optical system having an angle of view of 120 ° to 150 ° is not necessarily required. Regarding the NA of a single fiber (indicated by NA (S)), the larger the NA (S), the larger the angle of A that can be totally reflected by the core and the cladding, and can be used for an observation system with a wider angle of view. .

In the description so far, the case where the incident angle of light from the light guide is analyzed as representative of 0 ° has been described, but the NA of the light guide (indicated by NA (L)) has been described.
Since the light distribution characteristic as shown in FIG. 6 is obtained in the range of (3), if the following condition (3) is satisfied, the light distribution characteristic does not deteriorate for the observation system. (3) | NA (S) −sin | ω || <NA (L) / 2 where ω is a half angle of view of the observation optical system.

When the value exceeds the range of the condition (3), the light beam is not totally reflected at the boundary between the core and the clad, and the loss of light amount is too large, which is not preferable.

Also, the light distribution surface is insufficient for the illumination lens for the field angle 2ω of the observation optical system.

Depending on the state of the core and the cladding of the single fiber, molding may be difficult. For example the molding of a single fiber, for pressing from a high temperature until once the temperature of the glass above the transition point, the transition point between the core and the cladding is near the boundary of the core and the clad is deformed, causing the light distribution unevenness Become. Therefore, in order to minimize the deformation of the clad shape, the transition point of the core should be T (C
O), assuming that the transition point of the clad is T (CL), it is preferable that the following relationship is satisfied, since the clad is not deformed. T (CO) <T (CL) Next, the shape of the illumination lens used in the present invention will be described. Here, a plano-concave lens will be described for easy thinking. In that case, only the concave surface has power, that is, affects the hA curve.

When the condition (1) is satisfied, it is necessary to have an intensity distribution as shown by curves a and b in FIG. In order to achieve such a distribution on one aspherical surface, the curvature is gradually reduced as the distance from the optical axis is increased, and no inflection point is provided.

FIG. 7 is a diagram showing the above-mentioned contents, and shows the deviation amount Δx of the aspherical surface with respect to the paraxial spherical surface in the range in which the angle θ between each part of the aspherical surface and the optical axis monotonically decreases. It increases monotonically within.

In order to satisfy the condition (2), as shown in FIG. 5, it is necessary that R1> R2 and that R1 has a shape capable of improving the peripheral light distribution. The following conditions must be satisfied. (4) 0.4 ≦ h2 / h1 ≦ 0.8 If the upper limit of the above condition (4) is exceeded, the contribution of the peripheral light distribution by R1 becomes too small, and becomes the same as the light distribution characteristic by only R2. I will. When the lower limit of the above condition is exceeded, FIG.
The light distribution unevenness is likely to occur because S1 at the point of view starts to affect from a low angle of view.

Within the range that satisfies the above condition (4), cos ³ A is applied when finally evaluated on a plane, so that light distribution unevenness is at an acceptable level.

[0046]

Next, an embodiment of the illumination optical system according to the present invention will be described.

As shown in FIG. 8, the illumination lens of the first embodiment has an aspherical surface having a negative power on the side of the light guide .

This aspheric surface is represented by the following equation.

Here, x and y are coordinate values obtained by taking the direction of the light guide in the positive direction with respect to the optical axis as the x axis, and taking the y axis in the direction orthogonal to the x axis with the intersection point between the plane and the optical axis as the origin. C
Is the reciprocal of the radius of curvature of the spherical surface in contact with the aspherical surface near the optical axis, P is a parameter representing the shape of the aspherical surface, B, E,
F, G,... Are second-order, fourth-order, sixth-order, eighth-order,. When P = 1 and B, E, F, G,... Are all 0, the above equation represents a spherical surface.

The lens data of the first embodiment is as follows. R = 0.61, P = 0.1, E = −0.13 FIG. 13 shows the hA characteristics of the first embodiment.

In the first embodiment, d ² A / dh ² ≧ 0 and 0 <h <1 in order to improve the light distribution characteristics as compared with the conventional example.
A (h1) when h1 ≠ h2 to prevent uneven light distribution in the range
≠ A (h2).

Therefore, the aspherical shape has no inflection point and the curvature at the center becomes gentler toward the periphery.

In this embodiment, a single fiber is used as the illumination lens, but this lens is bonded to the frame using an adhesive having a refractive index of 1.4 to 1.6 instead of the clad. For example, an aspheric lens may be used instead of a single fiber.

By wedges as shown in FIG. 9 at the center of the light guide, the number of light rays directed toward the center having a small A can be reduced, and the light distribution to the periphery can be relatively increased.

The same effect can be obtained by separating the single fiber portion and the aspherical portion as shown in FIG.
When a lens having an aspherical surface is made by a press, it is difficult to make it in the state of a single fiber, so that it is effective to make it separately.

Embodiment 2 has an illumination lens having the configuration shown in FIG. In this embodiment, an aspheric surface is used for the convex surface, but the refractive indices of the core and the clad are the same as those of the first embodiment. The hA characteristics are the same as those of the first embodiment shown in FIG. 13, and an illumination system having good light distribution characteristics without uneven light distribution can be obtained.

In the second embodiment as well, it is possible to replace the clad with an adhesive, increase the light distribution by inserting a wedge into the light guide, and separate the single fiber and the aspherical portion.

The data of the aspherical surface of this embodiment is as follows. R = −0.55, P = 0.1, E = 0.2 The third embodiment is shown in FIG.
(A) up to (= 0.74) spherical surface, h (a) to h (b)
Until (= 1.105), it is an aspheric surface of the following data . R = 0.61, P = 0.105, E = -0.0915 The refractive index of the core is about 1.8, and the refractive index of the cladding is about 1.52.

The hA characteristic of the third embodiment is as shown in FIG. 14, where S (a) is a characteristic up to h (a) and S (b) is h (b).
The characteristics up to. Since the portion of S (a) satisfies d ² A / dh ² > 0, the light distribution particularly on the wide-angle side can be enhanced by S (b).

FIG. 15 shows the calculation result of the light distribution. FIG.
In FIG. 5, S (a) is the spherical light distribution characteristic of the portion of S (a) in FIG. 14, and S (b) of FIG. 15 which is the spherical light distribution characteristic of the portion of S (b) in FIG. Have joined. S is a light distribution characteristic on a plane obtained by multiplying the total spherical light distribution characteristic by cos ³ A.

[0061]

The endoscope illumination optical system according to the present invention is used for an ultra-wide-angle endoscope, and can provide an illumination that is bright up to the periphery of the visual field, has a small loss of light amount, and has no illumination unevenness.

[Brief description of the drawings]

FIG. 1 is a diagram showing a basic configuration of the present invention.

FIG. 2 is a diagram showing various patterns of a relationship (h-A characteristic) between a ray height and a refraction angle.

FIG. 3 is a diagram showing light distribution characteristics of an optical system having the above-mentioned pattern.

FIG. 4 is a diagram showing another hA characteristic.

FIG. 5 is a view showing an example of a lens having the characteristic curve.

FIG. 6 is a diagram showing light distribution characteristics of the lens.

FIG. 7 is a diagram showing a deviation of an aspheric surface from a paraxial spherical surface.

FIG. 8 is a sectional view of the first embodiment.

FIG. 9 is a cross-sectional view of the light guide of the above embodiment with a wedge provided at the center.

FIG. 10 is a cross-sectional view of an example in which the lens of the above embodiment is configured by combining a single fiber and an aspheric lens.

FIG. 11 is a sectional view of the second embodiment.

FIG. 12 is a sectional view of a third embodiment.

FIG. 13 is a diagram showing hA characteristics of Examples 1 and 2.

FIG. 14 is a graph showing hA characteristics of Example 3.

FIG. 15 is a diagram showing light distribution characteristics of the third embodiment.

FIG. 16 is a cross-sectional view of a conventional endoscope illumination optical system.

FIG. 17 is a diagram showing light distribution characteristics of the optical system.

FIG. 18 is a sectional view of another conventional example.

FIG. 19 is a diagram showing hA characteristics of the conventional example .

FIG. 20 is a diagram showing hA characteristics of another conventional example .

FIG. 21 is a diagram showing light distribution characteristics of the conventional example .

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Claims (3)

(57) [Claims] 1. An endoscope illumination optical system in which an illumination lens is arranged on an object side of an exit end of a light guide or a light emitting element, wherein the illumination lens is made of a single fiber having at least one aspheric surface, and Endoscope illumination optical system that satisfies the requirements. 0 <h <within 1 range, (1) when a d ² A / dh ² ≦ 0 when the h1 ≠ h2 A (h
1) ≠ A (h2) (2) When d ² A / dh ² > 0, A (h
1) Includes a portion where = A (h2). Here, h is a value obtained by standardizing the ray height of the light beam emitted parallel to the light guide axis by the maximum ray height, and A (h) is a ray height h that is parallel to the light guide axis.
Is the refraction angle measured from the optical axis after passing through the aspherical single fiber lens. 2. An endoscope illumination optical system in which an illumination lens is arranged on an object side of an emission end of a light guide or a light emitting element, wherein the illumination lens has an aspherical surface arranged on an emission end side of the light guide. And a single fiber disposed on the object side of the lens and satisfying the following condition. 0 <h <within 1 range, (1) when a d ² A / dh ² ≦ 0 when the h1 ≠ h2 A (h
1) ≠ A (h2) (2) When d ² A / dh ² > 0, A (h
1) Includes a portion where = A (h2). Here, h is a value obtained by standardizing the ray height of the light beam emitted parallel to the light guide axis by the maximum ray height, and A (h) is a ray height h that is parallel to the light guide axis.
Is the refraction angle measured from the optical axis after passing through the aspherical single fiber lens. 3. The endoscope illumination optical system according to claim 1, wherein the cladding of the single fiber is an adhesive.